What are these lines?

Transducer interference of some kind.
Is this a new problem?
Could be mechanical or electronic.
Where is your transducer mounted?

^^^This^^^
If on the TM the electronic interference. If on the transom possibly propwash

It’s on the transom.

They’re almost new units that I’m just getting around to messing with. I’ll have to see if I can do some trouble shooting.

Does it do it with the main motor off?

Got a pic of how your tranducer is mounted from the side and from the back looking at the transom?

You know, I’m not even sure. I was trying to sink some brush piles and got flustered that’s why I said I need to further trouble shoot.

When I do I’ll update this thread.

This looks like an interference issue to me. Try running your unit (on the lake) with every other electrical power device off and see if it does the same thing.That Ducer is picking up another signal boss. Could be troll mtr,live well pump etc.Turn everything OFF & if it does it still I`d contact Navico.

Given what I see and that this is on sidescan, my bet is that this is interference originating with reflected transducer signals, NOT electrical interference.
If you post a couple of photos of the transducer used for sidescan, we can comment more. We need to see where and how it is mounted, not just a close-up photo.